Neisseria meningitidis is the cause of epidemic bacterial meningitis. Capsular polysaccharide is a major virulence determinant of N. meningitidis. Among the 13 meningococcal serogroups classified based on capsular polysaccharide structure, serogroups A, B, C, Y, and W135 are associated with the majority of cases of meningococcal disease. In the African meningitis belt most large epidemics have been caused by serogroup A meningococci, whereas sporadic disease and outbreaks in developed countries are usually caused by serogroup B and C meningococci. Serogroup Y meningococci emerged as an important cause of sporadic disease and outbreaks in the United States in the late 1990s, and in 2000 serogroup W135 meningococci caused worldwide disease in association with the Hajj pilgrimage and large outbreaks in sub-Saharan Africa.
Serogroup X Neisseria meningitidis (MenX), previously a rare cause of sporadic cases of meningitis, has recently been associated with increased incidence of meningococcal disease and has emerged as a cause of large outbreaks in the “Meningitis Belt” of Africa. Outbreaks have been documented in Niger, Burkina Faso, Togo and Ghana and have varied in size. In the meningitis season of 2010 over 6500 meningitis cases were reported in Burkina Faso, and it is reasonable to assume that at least 1000 of these cases were due to MenX with a locally reported incidence of 120 cases per 100,000. Earlier, several patients were confirmed with MenX disease in an outbreak of at least 82 cases of bacterial meningitis on the border of Kenya and Uganda in 2007.
The capsular polysaccharides of serogroup B, C, Y, and W135 meningococci are composed of sialic acid derivatives. Serogroup B and C meningococci express (α2-8)- and (α2-9)-linked polysialic acid, respectively, while alternating sequences of D-glucose or D-galactose and sialic acid are expressed by serogroup Y and W135 N. meningitidis. In contrast, the capsule of serogroup A meningococci is composed of (α1-6)-linked N-acetylmannosamine 6-phosphate, while N. meningitidis serogroup X synthesizes capsular polymers of (α1-4)-linked N-acetylglucosamine 1-phosphate.
The increase in incidence of MenX disease in African Meningitis Belt in the last 5 years warrants development and introduction of a MenX vaccine in selected areas of the region to prevent and control future epidemics. The conjugation of meningococcal capsular polysaccharides to a carrier protein has led to the development of monovalent (A or C) polysaccharide conjugate vaccines with high effectiveness, and immunogenicity data from clinical trials indicate that wide use of tetravalent conjugate vaccines covering serogroups A, C, Y and W-135 may be similarly effective. A similar approach may also be fruitful for MenX. Refer Ouli Xiea et al “Characterization of size, structure and purity of serogroup X Neisseria meningitidis polysaccharide, and development of an assay for quantification of human antibodies”, Vaccine 30, 2012.
Gunnstein Norheim discusses that at present vaccine against serogroup X is not available and that next generation affordable vaccines should target most prevalent serogroups: A, W-135, X. Refer “Preventing the emerging serogroup X meningococcal disease in the African. Meningitis Belt” Oxford Vaccine Group, 2011.
The lack of a vaccine against group X meningococci is a cause for concern given the outbreaks caused by meningococci of this serogroup in the past few years. Refer “Meningococcal vaccines: WHO position paper”, November 2011.
In order to facilitate Men X polysaccharide based conjugate vaccine development, it is necessary to obtain structurally intact Men X polysaccharides with higher yields.
Several synthetic media were discovered for large-scale production of meningococcal polysaccharide (Frantz, I. D. Jr. Growth Requirements of the Meningococcus. J. Bact., 43: 757-761, 1942; Catlin, B. W. Nutritional profiles of Neisseria lactamica, gonorrhoeae and meningitidis, in chemically defined media. J. Inf. Dis., 128(2): 178-194, 1973; Watson-Scherp Medium: Watson R G, et al. The specific hapten of group C (group IIa) meningococcus, II. Chemical nature. J Immunol 1958; 81:337-44; Marcelo Fossa da Paz; Júulia Baruque-Ramos; Haroldo Hiss; Márcio Alberto Vicentin; Maria Betania Batista Leal; Isaías Raw. Polysaccharide production in batch process of Neisseria meningitidis serogroup C comparing Frantz, modified Frantz and Catlin 6 cultivation media, Braz. J. Microbiol. vol. 34., no. 1. São Paulo January/April 2003).
U.S. Pat. No. 5,494,808 reports a large-scale, high-cell density (5 g/L dry cell weight, and an optical density of between about 10-13 at 600 nm) fermentation process for the cultivation of N. meningitidis(serogroup B 11). This patent disclose the following medium (called “MC.6”) for culturing Neisseria meningitidis for isolation of OMPC (“Outer Membrane Protein Complex”)
U.S. Pat. No. 7,399,615 discloses a fermentation composition wherein the composition omits NH4Cl, and an improved method′ of fermenting Neisseria(serogroups A, C, Y & W135) in a fermentation composition replaces ammonium chloride(nitrogen source) with a soy peptone(HSP-A; Nutricepts, Inc; Minneapolis, Minn.). The said fed batch fermentation(2 L), wherein the fermentation medium as well as feed solution contains HSP-A results in Men A polysaccharide yield of about 1300-1400 mg/l at an average max OD between 14-20.
U.S. Pat. No. 7,491,517 discloses a Neisseria meningitidis fastidious culture medium (NMFM) for producing capsular polysaccharides from Neisseria meningitidis(serogroups A, C, Y & W135) comprising: DI (deionizer) water, NaCl, K2SO4, KCl, trisodium citrate.2H2O, MgSO4.7H2O, MnSO4.H2O, MnCl2.6H2O, vitamin. B12, NAD (Nicotinamide Adenine Dinucleotide) thiamine HCl, soy peptone, D-glucose, L-glutamic acid, L-arginine, L-serine, L-cysteine, glycine, morpholinepropanesulphonic acid [MOPS], CaCO3 to maintain pH at 6.5 to 7.0 and Fe2(SO4)3 for serogroup A and NH4Cl for serogroup W-135. The said fermentation results in polysaccharide yield of about 30-40 mg/L at an average max OD of 10.
David Bundle et al discusses preparation and isolation of Men X polysaccharide from N. meningitidis strain 247 X(Laboratory Center for Disease Control) wherein said strain was grown on a chemically defined medium (NCDM) for 18 hours. The said fermentation results in Men X polysaccharide yield of about 20 mg/L. Refer “Studies on the Group-specific Polysaccharide of Neisseria meningitidis Serogroup X and an improved Procedure for its isolation” JBC, 1974.
Ouli Xiea et al discloses preparation of MenX PS from strains BF7/07 and BF12/03. Briefly, the MenX strains were grown on Brain Heart Infusion agarplates with Levinthals' supplement, and following a pre-culturestep in 0.2 L Franz medium, the strain was cultivated in four separate 2.8 L baffled shaking flasks containing 1.0 or 1.5 L modified Franz liquid medium each. Liquid cultures were inactivated after 16 h of growth by adding formaldehyde to a final concentration of 1% (v/v). MenX PS yield per liter of growth medium appeared to be slightly higher for isolate BF 7/07 (4.5 mg/L) than for isolate BF12/03 (3.8 mg/L). Refer “Characterization of size, structure and purity of serogroup X Neisseria meningitidis polysaccharide, and development of an assay for quantification of human antibodies”, Vaccine 30, 2012.
Prior art discusses structural and yield improvement studies with respect to polysaccharides from serogroups Men A, C, Y & W135. However none of the prior art addresses the long felt need for preparation of Men X polysaccharide with higher yield which is a prerequisite for development of Men X plain polysaccharide and Men X polysaccharide protein conjugate vaccines.
Present inventors have found that prior art feeding strategies based on pH stat, spiking and constant rate which are suitable for Men A C Y W135 fermentation, however suffer from following setbacks for Men X: i) satisfactory growth but less polysaccharide yield ii) growth limiting, less polysaccharide yield and iii) satisfactory growth but early decline phase. Further prior art methods employ soya peptone & yeast extract as feed medium components that result in lower polysaccharide yield associated with increased load of protein contaminants.
It is an object of the present invention to provide improved culture, fermentation and purification conditions for preparing Neisseria meningitidis X polysaccharides with high yield and minimum impurities With said improvements, Men X polysaccharide protein conjugate vaccine manufacturing can be economical and subsequently vaccine can be made available to children of developing countries at an affordable rate.